Control circuit of a DC fan motor for start with high voltage and high rotational speed with low voltage

ABSTRACT

A control circuit of a DC fan motor for start with high voltage and high rotational speed with low voltage at least includes an input unit, an output unit, a control unit and a comparator. The input unit is connected to the comparison unit and the control unit for the power being inputted to operate the control circuit. The output unit has motor coil sets to be connected to the control unit such that the output unit can be driven by way of being controlled with the control unit. The comparison unit is connected to the control unit to control output current of the control unit. Hence, while the motor starts in a condition of being high voltage, the control element can prevent from being burned out due to excessively large current. Further, the motor fan can maintain a high constant rotational speed with low voltage output to enhance capability of heat dissipation and power saving.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is related to a control circuit of a DC fan motorfor start with high voltage and high rotational speed with low voltageand particularly to a control circuit preventing the control element ofa motor from damage.

2. Brief Description of the Related Art

Due to highly development of information technology in our society, itis a required function of the electronic product is that a great deal ofelectronic data can be transmitted and treated effectively. However, aside effect of occurring a phenomenon of generating high temperaturealways comes with the function. Hence, it is necessary for theelectronic product to provide a heat dissipation apparatus withexcellent performance and needing less power in order to solve theproblem of heat dissipation.

Currently, the cooling fan and the radiator are heat dissipationapparatuses available on the market are cooling fans and radiators. Theformer helps to dissipate heat by way of convection and the latterdissipates heat by way of conduction. Because forced heat dissipationcreated with the cooling fan provides better effect, the cooling fan iskept developed by all suppliers.

Referring to FIG. 1, a conventional circuit of a fan motor includes amotor 11 and a driving unit 12. The motor 11 includes at least a firstcoil set 111 and a second coil set 112. The driving unit 12 is connectedto the motor 11 and at least includes a driving element 121 and a Hallelement 122. The Hall element 122 senses magnetic pole changes of arotor in the motor 11 to generate positive voltage H+ and negativevoltage H− outputs corresponding and connected to corresponding pins.The driving element 121 has a first output pin 1211 connecting with thefirst coil set 111 and has a second output pin 1212 connecting with thesecond coil set 112 to actuate the motor 11 in running.

However, the preceding conventional circuit has problems in practice.Once the conventional circuit has been designed completely, thecharacteristic of the motor 11 is fixed. That is, the input voltage andthe rotational speed of the motor have a relation of proportion to eachother as the T1 curve shown in FIG. 2. For instance, when the inputvoltage is 12 volts, the rotational speed of the DC fan motor 11 is4,000 rpm and when the input voltage is 4 volts, the rotational speed ofthe DC fan motor is 1,000 rpm. Under this circumstance, the rotationalspeed with defined input voltage becomes a little too low and it is notpossible to attain the required heat dissipation effectively.

In order to increase rotational speed with low input voltage, the coilsets were redesigned to allow the DC fan motor 11 provides a rotationalspeed of 2,300 rpm with input voltage of 4 volts. However, the highinput voltage leads to increased rotational speed as well, i.e., 12volts with 8,000 rpm as T2 curve shown in FIG. 2. High rotational speedmeans increasing current and the phenomenon of burning out can occureasily in case of the increased current exceeding a range of currentcapable of being endured with the driving element 121.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a control circuit of aDC fan motor for start with high voltage and high rotational speed withlow voltage with which the power can be saved and the heat dissipationeffect can be enhanced.

Another object of the present invention is to provide a control circuitof a DC fan motor for start with high voltage and high rotational speedwith low voltage with which the fan motor can provide high rotationalspeed with low output voltage and the rotational speed can be maintainedin a state of high rotational speed with high output voltage, that is,the driving current can be kept in a range of safety values preset withthe control element to prevent the fan motor from damage resulting fromexcessively large current during being started to burn out the controlelement.

Accordingly, the control circuit of a DC fan motor for start with highvoltage and high rotational speed with low voltage according the presentinvention at least includes an input unit, an output unit, a controlunit and a comparator. The input unit is connected to the comparisonunit and the control unit for the power being inputted to operate thecontrol circuit. The output unit has motor coil sets to be connected tothe control unit such that the output unit can be driven by way of beingcontrolled with the control unit. The comparison unit is connected tothe control unit to control output current of the control unit. Hence,while the motor starts in a condition of being high voltage, the controlelement incapable of being burned out due to excessively large current.Further, the motor fan can maintain a high constant rotational speedwith low voltage output to enhance capability of heat dissipation andpower saving.

BRIEF DESCRIPTION OF THE RAWINGS

The detail structure, the applied principle, the function and theeffectiveness of the present invention can be more fully understood withreference to the following description and accompanying drawings, inwhich:

FIG. 1 is a conventional circuit diagram of a fan;

FIG. 2 is a graph illustrating characteristic curve of a conventionalfan motor;

FIG. 3 is a block diagram of circuit according to the present inventionin a preferred embodiment thereof;

FIG. 4 is a circuit diagram of the preferred embodiment according to thepresent invention; and

FIG. 5 is a graph illustrating characteristic curve of the preferredembodiment according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 2, it can be seen in the block diagram that thecontrol circuit of a DC fan motor for start with high voltage and highrotational speed with low voltage according to the present invention atleast includes an output unit 24, a control unit 23 connected to theoutput unit 24 directly, a comparison unit 22 connected to the controlunit 23 to control the control unit 23 outputting current and an inputunit 21 connected to the control unit and the comparison unit 22 forpower input.

Referring to FIGS. 3 and 4, the circuit of the preferred embodimentaccording to the present invention illustrated. The output unit 24 atleast includes a first motor coil set 241 and a second motor coil set242. The control unit 23 at least includes a control element 231 and aHall element 232. The Hall element 232 can sense the magnetic polechanges of a rotor in the control unit 24 to generate positive voltageH+ output and negative voltage H− output and the Hall element 232 isconnected to the IN+ pin and IN− pin of the control elementcorresponding to the positive voltage H+ and the negative voltage H−respectively. The control element 231 has a first output pin OUT1connected to the first motor coil set 241 and has a second output pinOUT2 connected to the second motor coil set 242 so as to control andactuate the output unit 24. The comparison unit 22 at least includes acomparator 221 (or an operation amplifier) and the comparator 221 has apositive phase input end 2211, a negative phase input end 2212 and anoutput end 2213. The output end 2213 is connected to a VTH pin of thecontrol element 231 and a resistor 222 and a stabilizing element 223 areprovided between the output end 2213 and the VTH pin. The resistor 222at one end thereof is for inputting DC power source and another endthereof is connected to the output end 2213. The stabilizing element 223at one end thereof is grounded and another end thereof is connected tothe output end 2213. The positive phase input end 2211 is connected to aresistor 224, a resistor 225 and a capacitor 226 and the resistor 224 atone end thereof is for inputting the DC power source and at another endthereof is connected to the positive phase input end 2211. Further, theresistor 225 at one end thereof is grounded and anther end thereof isconnected to the positive phase input end 2211 and the capacitor 226 atone end thereof is grounded and at another end thereof is connected tothe positive phase input end 2211. The negative phase input end 2212 isconnected to a resistor 227 and a stabilizing element 228 and theresistor 227 at one end thereof is inputted with the DC power source andat another end thereof is connected to the negative phase input end2212. The stabilizing element 228 at one end thereof is grounded and atanother end thereof is connected to the negative phase input end 2212,that is, the negative phase input end 2212 of the comparator 221receives branch voltage signal consisting of the resistor 227 and thestabilizing element 228 and the preceding stabilizing elements 223, 228can be Zener diodes.

The input unit 21 is provided for being inputted with an input powersource Vcc and includes a reversed voltage protect diode 211 to connectwith the comparison unit 22 and the control unit 23 for admitting the DCpower source.

When the power source Vcc inputs via the input unit 21, the current cantransmitted to the comparison unit 22 and the control unit 23 via thereversed voltage protect diode 211. The resistors 224 and 225 of thepositive phase input end 2211 in the comparator 221 generate branchvoltage signal received by the capacitor 226 to perform charging anddischarging such that the voltage signal inputted via the positive phaseinput end can vary in a range of constant value. When the signal at thepositive phase input end 2211 is less than branch voltage signal of thenegative phase input end 2212, the output end 2213 of the comparator 221generates a negative phase signal and the control element 231 resiststhe driving signal (driving current) from being sent to the output unit24 in case of the VTH pin of the control element 231 receiving thenegative phase signal.

When the input signal at the positive phase input end 2211 is greaterthan the branch voltage signal at the negative phase input end 2212, theoutput end 2213 of the comparator 221 generates a positive phase signaland the fan motor starts with high voltage in case of a large differencebetween the positive phase signal and the negative phase signal beingprovided. Due to the outputted positive phase signal being large, thestabilizing element 223 stabilizes the positive phase signal in a rangeof constant voltages by way of the function of branch voltage of theresistor 222 and stabilizing element 223 at the output end 2213. Whenthe VTH pin of the control element 231 receives positive phase signal, adriving signal (driving current) can be sent the first coil set 241 andthe second coil set 242 via the first output pin OUT1 and the secondoutput pin OUT2 so as to actuate the output unit 24 rotating with highspeed.

When the positive phase difference between the input voltage signal atthe positive phase input end 2211 and the branch signal at the negativephase input end 2212 is small, the fan motor rotates with low voltageand the output positive phase signal has low voltage. Due to function ofthe branch voltage of the resistor 222 and the stabilizing element 223,the stabilizing element 223 stabilizes the positive phase signal in arange of constant voltages. When the VTH pin of the control element 231receives positive phase signal, the current is sent the first coil set241 and the second coil set 242 via the first output pin OUT1 and thesecond output pin OUT2 so as to allow the output unit 24 rotating withconstant speed.

Referring to FIGS. 4 and 5, an example of the preferred embodimentaccording to the present invention is illustrated. When the fan motorstarts with outputting 12 volts high voltage and rotates with outputting4 volts low voltage, the comparison unit 22 generates a constantpositive phase signal to the VTH pin of the control element 231 andoutput currents via the first output pin OUT1 and the second output pinOUT2 are the same value in spite of different voltages, i.e., the highvoltage and the low voltage. In this way, the rotational speed of theoutput unit 24 is 2,300 rpm constantly to overcome the problem ofexcessive load resulting from high rotational speed with low voltageoutput and start with high voltage output so as to avoid burned-out.Further, it can reduce power waste and enhance heat dissipationefficiency under low voltage operation.

While the invention has been described with referencing to a preferredembodiment thereof, it is to be understood that modifications orvariations may be easily made without departing from the spirit of thisinvention, which is defined by the appended claims.

1-11. (canceled)
 12. A control circuit for a DC fan motor being capable of keeping a high rotational speed constantly, which DC fan motor is started with high voltage and runs with low voltage, comprising: an input unit, providing a reversed voltage protect diode and supply power to the circuit; an output unit, providing at least a first motor coil set and a second motor coil set; a control unit, providing a control element and a Hall element, wherein, the control element further comprises a plurality of pins and part of the pins connect with the input unit, the first and second motor sets and the Hall element; characterized in that a comparison unit is provided to connect with the input unit and the control unit respectively and the comparison unit further comprises: an operation amplifier, providing a positive phase input end, a negative phase end and an output end and the output end being connected to one of the pins in the control element; a first resistor, being connected to the positive phase input end and connected to the input unit via the reversed voltage protect diode; and a second resistor, being disposed parallel to the first resistor, being connected to the negative phase input end and connected to the input unit via the reversed voltage protect diode too; a third resistor, being connected to the positive phase input end to generate a positive phase input signal with the first resistor to enter the operation amplifier via the positive phase input end; a first stabilizing element, being connected to the negative phase input end to generate a negative phase input signal with the second resistor to enter the operation amplifier via the negative phase input end; a fourth resistor, being connected to the output end of operation amplifier to generate a branch voltage signal; a second stabilizing element, being connected to the output end to stabilize a positive phase output signal of the operation amplifier before entering the control element; and a capacitor, being connected to the positive phase input end to perform charging and discharging for regulating the positive phase input signal being in a range of constant values; wherein, when the positive phase input signal is greater than the negative phase input signal and a difference between the positive phase input signal and the negative phase input signal is large, the positive phase output signal is large such that a driving current is sent to the output unit for the output unit being started with a high speed once the control element receives the positive phase output signal; when the positive phase input signal is greater than the negative phase input signal but the difference between the positive phase input signal and the negative phase input signal is small, a small positive phase output signal is sent out by the operation amplifier and stabilized with the second stabilizer and the branch voltage signal before being sent to the control element such that the driving current is sent to the output unit for the output unit running with a speed same as the high speed constantly once the stabilized positive phase output signal is sent to the control element. 